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  <!-- 1. 封装函数, 名字为sum
  2. 功能: 根据传入的两个数,求和并且返回求和的结果（函数必须有return返回值）
  先不要看答案哦~~~ -->
  <script>
    function sum(x = 0, y = 0) {
      let he = x + y
      return he
    }
    let getSum = sum(11, 22)
    document.write(getSum)
  </script>

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